Power supply control system

ABSTRACT

The present invention provides a power supply control system comprising a first switch circuit configured to set a power supply line which connects a power supply unit and a power supply circuit to one of a connected state and a non-connected state, a first control unit configured to operate in one of a normal mode and a sleep mode in which a consumption current is smaller than in the normal mode, and to detect a magnitude of a current flowing into the first switch circuit and control an operation of the first switch circuit based on the detected magnitude of the current while operating in the normal mode, and a second control unit configured to control an operation of the first control unit based on the detection result of an opening-closing state detection unit configured to detect an opening-closing state of a battery lid provided to the power supply unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 12/188,348,filed Aug. 8, 2008 the entire disclosure of which is hereby incorporatedby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a power supply control system whichcontrols a power supply voltage supplied from a power supply unit to aload circuit.

2. Description of the Related Art

In recent years, a digital camera and digital video camera are becomingprevalent as image capture apparatuses. These cameras form an image oflight from an object on an image capture element via an optical lens,thereby capturing and recording a digital image of the object. Suchimage capture apparatuses include a power supply control system whichcontrols power supply voltages supplied to load circuits such as acircuit for driving the optical lens and that for operating the imagecapture element (see Japanese Patent Laid-Open No. 7-288930).

Japanese Patent Laid-Open No. 7-288930 discloses a power supply controlsystem in which a fuse is inserted in a power supply line which suppliespower supply voltages (DC voltages) from a power supply circuit (DC-DCconverter) to a plurality of load circuits. When an overcurrent flowsinto the power supply line as the load circuit, DC-DC converter, or thelike short-circuits, such a power supply control system disconnects thepower supply line by the fuse so that the supply of a power supplyvoltage to the short-circuited device can be stopped without anyinfluence such as voltage fluctuation on the other load circuits.

A power supply control system as shown in FIG. 3 has also been known.FIG. 3 is a schematic block diagram showing the configuration of aconventional power supply control system 1000. In FIG. 3, a power supplyunit 1010 includes a battery, and a power supply circuit 1020 includes aDC-DC converter. DC voltages output from the power supply circuit 1020are applied to load circuits 1070, 1080, and 1090 as DC power supplyvoltages for operating them. A current detection resistance 1040 andcurrent limiting resistance 1050 are connected in series with each otherbetween the power supply unit 1010 and the power supply circuit 1020.

The two ends of the current detection resistance 1040 are connected to acurrent determination circuit 1032 included in a control unit 1030. Thecontrol unit 1030 includes a control circuit 1034 which receives theoutput from the current determination circuit 1032. The operating powersupply voltage of the control unit 1030 is directly supplied from thepower supply unit 1010. A shutoff switch (SW) circuit 1060 is connectedin parallel with a current limiting resistance 1050. The shutoff switchcircuit 1060 is controlled in accordance with a control signal from thecontrol circuit 1034. The control signal from the control circuit 1034is also supplied to the power supply circuit 1020, and used to controlthe power supply circuit 1020 to an operative state.

However, the power supply control system requires a large consumptioncurrent in operation, so the consumption current of the power supplycontrol system is preferably minimized when the image capture apparatusis not used.

A general image capture apparatus has a battery lid to preventdetachment of a battery serving as a power supply. Even while thebattery lid is open, a power supply voltage is often supplied to theimage capture apparatus as long as the battery is attached to the imagecapture apparatus. In this case, the power supply control system is in asleep state while the battery lid is open. However, because an abnormalcurrent cannot be monitored while the power supply control system is ina sleep state, a fuse must be inserted in the power supply line. Oncethe fuse blows out, it must be replaced with a new one. It is difficultand inconvenient to replace a fuse in a compact apparatus such as animage capture apparatus. However, when the power supply control systemis always kept in a normal state, it wastefully consumes the power ofthe battery.

SUMMARY OF THE INVENTION

The present invention to provides an electronic apparatus which enablesan abnormal current check even while a battery lid is open without usingany fuse, and suppresses the consumption of a power supply by a powersupply control system itself.

According to one aspect of the present invention, there is provided Apower supply control system comprises: a power supply circuit configuredto supply a DC voltage output from a power supply unit which detachablyholds a battery to a load circuit; a first switch circuit configured toset a power supply line which connects the power supply unit and thepower supply circuit to one of a connected state and a non-connectedstate; a first control unit configured to operate in one of a normalmode and a sleep mode in which a consumption current is smaller than inthe normal mode, and to detect a magnitude of a current flowing into thefirst switch circuit and control an operation of the first switchcircuit based on the detected magnitude of the current while operatingin the normal mode; an opening-closing state detection unit configuredto detect an opening-closing state of a battery lid provided to thepower supply unit; and a second control unit configured to control anoperation of the first control unit based on the detection resultobtained by the opening-closing state detection unit, wherein if theopening-closing state detection unit detects that the opening-closingstate of the battery lid is an opening state, the second control unitoperates the first control unit in the normal mode to detect themagnitude of the current flowing into the first switch circuit.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram showing a power supply controlsystem according to one aspect of the present invention;

FIG. 2 is a flowchart for explaining the operation of the power supplycontrol system according to one aspect of the present invention; and

FIG. 3 is a schematic block diagram showing a conventional power supplycontrol system.

DESCRIPTION OF THE EMBODIMENT

A preferred embodiment of the present invention will be described belowwith reference to the accompanying drawings.

FIG. 1 is a schematic block diagram showing a power supply controlsystem 1 according to one aspect of the present invention. The powersupply control system 1 controls power supply voltages supplied to aplurality of load circuits LC₁, LC₂, and LC₃, and is suitable for imagecapture apparatuses such as a digital camera. The plurality of loadcircuits LC₁, LC₂, and LC₃ include, for example, a circuit for drivingan optical lens, that for driving an electronic flash, and that foroperating an image capture element. However, the power supply controlsystem 1 is applicable not only to image capture apparatuses but also tovarious electronic apparatuses.

As shown in FIG. 1, the power supply control system 1 includes a powersupply unit 10, battery lid 12, control unit 20, first switch circuit30, current detection resistance 40, system control unit 50, powersupply circuit 60, current limiting resistance 70, and second switchcircuit 80.

The power supply unit 10 detachably holds a battery (commonly-usedbattery, dedicated battery, or battery holder), and outputs a DCvoltage.

The battery lid 12 is provided to the power supply unit 10, and preventsthe battery attached to the power supply unit 10 from jumping out of thepower supply unit 10. The battery lid 12 includes an opening-closingstate detection unit 14 which detects its opening-closing state. Theopening-closing state detection unit 14 includes a detection switch andcircuit for detecting the opening-closing state of the battery lid 12,and outputs a detection signal representing the opening-closing state ofthe battery lid 12 to the control unit (second control unit) 20.

The control unit 20 controls the operation of the system control unit 50based on the detection result (detection signal) obtained by theopening-closing state detection unit 14. The control unit 20 includes atimer circuit which measures the time elapsed since the battery lid 12opens (predetermined time). The control unit 20 also controls theoperations of the second switch circuit 80 and power supply circuit 60based on the detection result (the magnitude of a current flowing intothe first switch circuit 30) which is obtained by a current detectioncircuit 52 and input from the system control unit 50 (control circuit54). The detailed control of units by the control unit 20 will bedescribed in detail later.

The first switch circuit 30 has a function of setting a power supplyline which connects the power supply unit 10 and the power supplycircuit 60 to a connected state or non-connected state. One terminal ofthe first switch circuit 30 is connected to the terminal of the powersupply unit 10, which outputs a DC voltage supplied from it, via thecurrent detection resistance 40. The other terminal of the first switchcircuit 30 is connected to the power supply circuit 60 via the currentlimiting resistance 70. The first switch circuit 30 may be connectedbetween the power supply circuit 60 and a parallel circuit of thecurrent limiting resistance 70 and second switch circuit 80.

The current detection resistance 40 is provided to detect the magnitudeof the current flowing into the first switch circuit 30. Because thecurrent detection resistance 40 is basically inserted immediately afterthe power supply unit 10, it can monitor (detect) the current magnitude(current value) of the overall system.

The system control unit (first control unit) 50 operates in a normalmode or a sleep mode in which the consumption current is smaller than inthe normal mode, and controls the operation of the first switch circuit30 based on the magnitude of the current flowing into the first switchcircuit 30. The operating power supply voltage of the system controlunit 50 is supplied from the middle point of the connection path betweenthe power supply unit 10 and the terminal of the current detectionresistance 40. In this embodiment, the system control unit 50 includesthe current detection circuit 52 and control circuit 54.

The current detection circuit 52 detects the magnitude of the currentflowing into the first switch circuit 30, and is connected to the twoends of the current detection resistance 40. More specifically, thecurrent detection circuit 52 monitors (detects) the voltage across thetwo ends of the current detection resistance 40, and calculates themagnitude (current value) of the current flowing into the first switchcircuit 30. If the magnitude of the current flowing into the firstswitch circuit 30 is equal to or larger than a predetermined threshold(i.e., an abnormal current is flowing through the power supply controlsystem 1), the current detection circuit 52 outputs to the controlcircuit 54 an abnormal current detection signal representing that anabnormal current is detected.

The control circuit 54 ON/OFF-controls the first switch circuit 30 basedon the detection result obtained by the current detection circuit 52.More specifically, if the magnitude of the current flowing into thefirst switch circuit 30 is equal to or larger than the threshold (if thecontrol circuit 54 receives the abnormal current detection signal), thecontrol circuit 54 turns off the first switch circuit 30 to set thepower supply line which connects the power supply unit 10 and the powersupply circuit 60 to a non-connected state. If the magnitude of thecurrent flowing into the first switch circuit 30 is smaller than thethreshold (i.e., the control circuit 54 receives no abnormal currentdetection signal), the control circuit 54 turns on the first switchcircuit 30 to set the power supply line which connects the power supplyunit 10 and the power supply circuit 60 to a connected state.

The power supply circuit 60 includes, for example, a DC-DC converter,and supplies, to the plurality of load circuits LC₁, LC₂, and LC₃, DCvoltages serving as their required operating power supply voltagesaccording to their specifications.

The current limiting resistance 70 is connected between the first switchcircuit 30 and the power supply circuit 60, and has a function oflimiting a DC voltage supplied to the power supply circuit 60. Thecurrent limiting resistance 70 has a function of ensuring the operatingvoltages of the control unit 20 and system control unit 50 (currentdetection circuit 52 and control circuit 54) when one of the powersupply circuit 60 and load circuits LC₁, LC₂, and LC₃ short-circuits.

The second switch circuit 80 is connected in parallel with the currentlimiting resistance 70, and inserted in the power supply line whichconnects the first switch circuit 30 and the power supply circuit 60.The second switch circuit 80 supplies a DC voltage to the power supplycircuit 60 by bypassing the current limiting resistance 70 in an ONstate. The second switch circuit 80 is OFF when a battery is attached tothe power supply unit 10. Therefore, a DC voltage from the power supplyunit 10 is limited and supplied to the power supply circuit 60 via thecurrent limiting resistance 70 until (a control signal from) the controlunit 20 turns on the second switch circuit 80.

The power supply control system 1 is formed by connecting the currentdetection resistance 40, first switch circuit 30, and current limitingresistance 70 in series with each other in this order from the powersupply unit 10 to the power supply circuit 60. The second switch circuit80 is connected in parallel with the current limiting resistance 70.Although each of the first switch circuit 30 and second switch circuit80 includes a switch which uses a semiconductor element such as an FETelement in this embodiment, it may include a switch element which uses amechanical solenoid.

In the power supply control system 1, the first switch circuit 30 isinserted immediately after the current detection resistance 40, in orderto shut off the overall system. The first switch circuit 30 and secondswitch circuit 80 are OFF while a battery is not attached to the powersupply unit 10.

When a battery is attached to the power supply unit 10, that is, a DCvoltage is supplied from the power supply unit 10, (a control signalfrom) a control unit (not shown) turns on the first switch circuit 30.The control unit 20 is also operated to set the system control unit 50in the normal mode or sleep mode in accordance with a detection signalrepresenting the opening-closing state of the battery lid 12 from theopening-closing state detection unit 14. More specifically, if theopening-closing state detection unit 14 detects that the opening-closingstate of the battery lid 12 is a closing state, the control unit 20operates the system control unit 50 in the normal mode. If theopening-closing state detection unit 14 detects that the opening-closingstate of the battery lid 12 is an opening state, the control unit 20temporarily operates the system control unit 50 in the normal mode tocheck an abnormal current, and then operates it in the sleep mode. Thismakes it possible to suppress the consumption of the power supply(battery drain) by the power supply control system 1 while the batterylid 12 is open, and detect an abnormal current. It is therefore possibleto suppress the consumption of the power supply due to the flow of anabnormal current. However, if the system control unit 50 is operated,and the detection result obtained by the current detection circuit 52reveals that an abnormal current is flowing, (a control signal from) thecontrol circuit 54 turns off the first switch circuit 30. In otherwords, if the magnitude of the current flowing into the first switchcircuit 30 is equal to or larger than the threshold, the first switchcircuit 30 is turned off to set the power supply line which connects thefirst switch circuit 30 and the power supply circuit 60 to anon-connected state.

If the detection result obtained by the current detection circuit 52reveals that the magnitude of the current flowing into the first switchcircuit 30 is smaller than the threshold, (a control signal from) thecontrol unit 20 turns on the second switch circuit 80. Then, (thecontrol signal from) the control unit 20 also operates the power supplycircuit 60, and a DC voltage output from the power supply unit 10 issupplied to the power supply circuit 60 by bypassing the currentlimiting resistance 70 (via the second switch circuit 80). This makes itpossible to prevent wasteful power consumption by the current limitingresistance 70 (suppress the consumption of the power supply).

The operation of the power supply control system 1 will be explainedbelow with reference to FIG. 2. FIG. 2 is a flowchart for explaining theoperation of the power supply control system 1. In this embodiment, thefirst switch circuit 30 and second switch circuit 80 are OFF until abattery is attached to the power supply unit 10, as described above.

In step S201, a battery is attached to the power supply unit 10. In stepS202, the control unit (not shown) turns on the first switch circuit 30.The control unit 20 is also operated to operate the system control unit50 in the normal mode.

In step S203, the control unit 20 determines the opening-closing stateof the battery lid 12. More specifically, the control unit 20 determineswhether the opening-closing state of the battery lid 12 is an openingstate or closing state, based on a detection signal which represents theopening-closing state of the battery lid 12 and is output from theopening-closing state detection unit 14. If the opening-closing state ofthe battery lid 12 is determined to be an opening state, the processadvances to step S204. If the opening-closing state of the battery lid12 is determined to be a closing state, the process advances to step5210.

In step S204, it is determined whether the battery lid 12 has been openfor 1 sec. If the battery lid 12 has been open for 1 sec, the processadvances to step S205. If the battery lid 12 has not been open for 1sec, the process returns to step S203.

In step S205, the current detection circuit 52 determines whether anabnormal current is flowing through the power supply control system 1.More specifically, if the magnitude of a current flowing into the firstswitch circuit 30 is equal to or larger than the threshold, the currentdetection circuit 52 determines that an abnormal current is flowing as,for example, one of the power supply circuit 60 and load circuits LC₁,LC₂, and LC₃ short-circuits. If the magnitude of the current flowinginto the first switch circuit 30 is smaller than the threshold, thecurrent detection circuit 52 determines that no abnormal current isflowing. If it is determined that an abnormal current is flowing, thecurrent detection circuit 52 outputs an abnormal current detectionsignal to the control circuit 54, and the process advances to step S206.If it is determined that no abnormal current is flowing, the processadvances to step S207.

In step S206, the control circuit 54 turns off the first switch circuit30 to end the operation. With this operation, the power supply linewhich connects the power supply unit 10 and the power supply circuit 60enters a non-connected state. This makes it possible to prevent theabnormal current from continuing flowing through the power supplycontrol system 1.

In step S207, the control unit 20 operates the system control unit 50 inthe sleep mode. In other words, the control unit 20 switches theoperation mode of the system control unit 50 from the normal mode to thesleep mode. With this operation, the system control unit 50 operateswith a small consumption current. This makes it possible to suppress theconsumption of the power supply.

In step S208, the control unit 20 determines the opening-closing stateof the battery lid 12, as in step S203. If it is determined that theopening-closing state of the battery lid 12 is an opening state, theprocess waits until the opening-closing state of the battery lid 12changes to a closing state. If it is determined that the opening-closingstate of the battery lid 12 is a closing state, the process advances tostep S210.

In step S210, the current detection circuit 52 determines whether anabnormal current is flowing through the power supply control system 1,as in step S205. If it is determined that an abnormal current isflowing, the current detection circuit 52 outputs an abnormal currentdetection signal to the control circuit 54, and the process advances tostep S211. If it is determined that no abnormal current is flowing, theprocess advances to step 5212.

In step S211, the control circuit 54 turns off the first switch circuit30 to end the operation. With this operation, the power supply linewhich connects the power supply unit 10 and the power supply circuit 60enters a non-connected state. This makes it possible to prevent theabnormal current from continuing flowing through the power supplycontrol system 1.

In step S212, the control unit 20 turns on the second switch circuit 80,and also operates the power supply circuit 60.

As the second switch circuit 80 is turned on and the power supplycircuit 60 is operated, the plurality of load circuits LC_(I), LC₂, andLC₃ normally operate in step S213. Since the second switch circuit 80 isON, it is possible to avoid wasteful power consumption by the currentlimiting resistance 70.

As the system control unit 50 operates in the normal mode, the currentdetection circuit 52 determines in step S214 whether an abnormal currentis flowing through the power supply control system 1. If it isdetermined that an abnormal current is flowing, the current detectioncircuit 52 outputs an abnormal current detection signal to the controlcircuit 54, and the process advances to step S215. If it is determinedthat no abnormal current is flowing, the process operation in step S214is repeated to continue the determination as to whether an abnormalcurrent is flowing through the power supply control system 1.

In step S215, the control circuit 54 turns off the first switch circuit30 to end the operation. With this operation, the power supply linewhich connects the power supply unit 10 and the power supply circuit 60enters a non-connected state. This makes it possible to prevent theabnormal current from continuing flowing through the power supplycontrol system 1.

As described above, the power supply control system 1 according to thisembodiment can suppress the consumption of the power supply (battery)due to the flow of an abnormal current and by the power supply controlsystem itself by controlling the operation of the power supply controlsystem in accordance with the opening-closing state of the battery lid.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2007-210298 filed on Aug. 10, 2007, which is hereby incorporated byreference herein in its entirety.

1. A power supply control system, comprising: a power supply unit thatincludes a detachable battery; a power supply circuit that supplies DCvoltage to a load; a first switch circuit that is connected in seriesbetween the power supply unit and the power supply circuit; a firstcontrol unit that operates in one of a first mode and a second mode inwhich a consumption current is smaller than in the first mode, whereinthe first control unit can determine whether or not a current flowinginto the first switch circuit is abnormal if the first control unit isoperated in the first mode, and the first control unit turns off thefirst switch circuit if the first control unit determines that thecurrent flowing into the first switch circuit is abnormal; anopening-closing state detection unit that detects whether a battery lidis one of an opening state and a closing state, wherein the battery lidis provided to the power supply unit; and a second control unit thatcontrols the first control unit to cause the first control unit tooperate in one of the first mode and the second mode, wherein if theopening-closing state detection unit detects that the battery lid is inthe opening state, the second control unit causes the first control unitto operate in the first mode before the second control unit causes thefirst control unit to operate in the second mode so that the firstcontrol unit can determine whether or not the current flowing into thefirst switch circuit is abnormal.
 2. The power supply control systemaccording to claim 1, further comprising: a timer circuit that measuresa time elapsed since the opening-closing state detection unit detectsthat the battery lid is in the opening state, wherein the second controlunit causes the first control unit to operate in the first mode if thetimer circuit measures a predetermined time.
 3. The power supply controlsystem according to claim 1, further comprising: a current limiting unitthat is connected between the first switch circuit and the power supplycircuit, and limits a current flowing between the first switch circuitand the power supply circuit; and a second switch circuit that isconnected in parallel with the current limiting unit, wherein the secondcontrol unit turns on the second switch circuit if the battery lid is inthe closing state and the first control unit determines that the currentflowing into the first switch circuit is not abnormal.
 4. The powersupply control system according to claim 3, wherein the first controlunit turns off the first switch circuit if the battery lid is in theclosing state, the first switch circuit and the second switch circuitare turned on, and the first control unit determines that the currentflowing into the first switch circuit is abnormal.